The present invention relates to a method of stabilizing an aluminum metal layer in an aluminum electrolytic cell. More particularly, the present invention relates to a method of decreasing horizontal currents occurred in an aluminum metal layer in an aluminum electrolytic cell to prevent the fluctuation and upheaval of metal layer to thereby stabilize the metal layer.
The electrolytic production of aluminum is industrially carried out by connecting plural rectangular electrolytic cells in series by anode buses and cathode buses to make up a pet line and passing a large current of 50 to 250 KA therethrough to electrolyze alumina in the electrolytic bath with direct current. As a method of connecting these electrolytic cells, two typical types, that is, single entry type in which cell currents drawn out from the both sides of an electrolytic cell to cathode buses are supplied to anode buses of the second cell from one side thereof and double entry type in which cell currents drawn out to cathode buses are supplied to anode buses of the second cell from the both sides thereof have been known. In either case, a srong magnetic field is generated in the interior of electrolytic cell because cathode buses which a high electric current flows through passes the side of cell.
On the other hand, in the electrolytic cell, currents introduced from anode buses are led to an electrolytic bath through carbon anodes, further reach a cathode bed of carbon via an aluminum metal layer, thereafter are collected by plural collector bars provided parallel to the end walls of container and are withdrawn to cathode buses provided along the both side walls of container. The cell currents pass through a short circuit course which is lowest in electric resistance toward collector bars so that a part of cell current flowing through the central parts of cell comes to take directly a course directing to collector bars in the neighborhood of the side walls of container without taking a vertically downward course, and, as the result, horizontal currents directing to the side walls of container from the longitudinal center line thereof are produced in the cell, particularly in the aluminum metal layer.
The horizontal currents produced in the aluminum metal layer fluctuate the layer and heave the upper surface of the layer by an interaction with the above described magnetic field. When the aluminum metal layer becomes thus unstable the layer contacts sometimes with the lower surface of carbon anode and the cell currents comes to flow through the contacting part thereby the current efficiency decreases remarkably.
Then, as the result of studying on a method of stabilizing an aluminum metal layer, the present inventor has found that, if the direction of current flowing through collector bars is controlled to a specific direction, the horizontal currents in the aluminum metal layer decrease and so the aluminum metal layer can be effectively stabilized, and have attained the present invention.